1. Field of the Invention
During the latest decade there has been an increased focus on the purification of waste water from urban and industrial activity prior to leading it back to nature.
Numerous isolated private housings are still not connected to public sewerage systems and their waste water is therefore not treated in a public purifying plant. Instead these housings have to rely on their individual solutions to the purification issue.
A common solution for one-family houses is in form of a septic tank in which an anaerobic fermentation process at low temperatures purifies the waste water. This process however takes a significant time and the outflow is often discharged to some kind of percolation through the ground, e.g. a seepage pit, or through a drainage tube, e.g. to the nearest lake or stream.
In Denmark alone more than 300.000 housings only rely on a septic tank for waste water treatment.
Recent demands from the authorities force such housings to provide improved purification of their waste water. Among others there are focus on organic compounds, phosphorous compounds and nitrogen containing compounds.
In many areas in which it is not feasible to be connected to a public sewerage system it is an option to provide individual solutions which, however would give rise to provision of a total excess capacity of the plants especially for concentrations of users in a limited geographical area. A simple scaling up in a common plant of would also require installation of an excess capacity of septic tanks in order to meet with the required holding time in the septic tank, in order that the plant can handle peak flows.
Still further, in sparely populated or remote areas the infrastructure is often poorly developed which complicates establishment of local or remote plants due to lack of roads or other means of communication.
2. Description of the Related Art
Various mini purification plants have been proposed, e.g. plants of the kind disclosed in WO 03/020650 (Kongsted Maskinfabrik) or WO 2005/026064 (Biokube). Such plants are delivered in the form of a package solution comprising a tank for containing the functional parts together with an assembly of the functional parts which are then assembled at the site where the plant is to be placed.
WO 98/23540 discloses waste-water treatment system for biological cleaning of waste-water from one or more households, institutions, recreation centres, business premises and the like, and for up to approx. 50 person equivalents (PE), said treatment comprising aeration and biological filtration of the waste-water, nitrification and chemical precipitation of phosphor. The miniature waste-water treatment system is characterized in that the system comprises a container with a solid filter element and a post-clarification zone, the system has elements) to lead air in counterblow in relation to the waste-water, a pump controlled by a level switch is provided in a pump well mounted on the side of the container, a time-controlled pump is arranged to dose waste-water to a precipitation chemical, and the system has elements to lead sludge which, by the aeration and chemical precipitation is deposited in the bottom of the container, to a sedimentation tank which is placed upstream from the system.
The system is rather complicated and demands a constant control and supply of e.g. chemicals and maintenance of pumps not always being available at remote sites. Furthermore, the lowermost part of the container consists of a truncated cone, the smallest diameter of which is disposed at the bottom in the container, concentrating the precipitated sludge in the truncated cone which renders a system exposed for clogging. Still further the system disclosed in WO 98/23540 requires a bottom comprising a fundament with a strong flange which has a greater diameter than the container in order to safeguard the system against buoyancy.
For remote sites, however, the delivery of tanks and assembly of the state of the art is associated with disproportionately high transportation and erection costs. Furthermore, such plants should be simple and require a minimum of control and maintenance.
The present invention offers a simple and reliable solution to these problems.